A woman who slipped into a crowded Catonsville barbersho moments before a gunman opened fire, killing the owner and a customer whose hair he was cutting, may hold the key to the strange execution-style slayings, authorities said yesterday.

Baltimore County police were searching for the woman, who disappeared when the lone gunman walked in early Saturday morning. The woman may have gestured toward the man in the chair, Michael Selwyn Peters, 20, of Woodlawn, who was shot in the head and died immediately, police and neighbors said.

James Ernest Brodie, 58, a retired school custodian who had operated barber shops in the Catonsville area for 30 years, died at the Maryland Shock Trauma Center shortly after the 6 a.m. attack. He was shot in the chest, police said yesterday.

Mr. Brodie lived in an apartment above his neat, small barbershop in the 400 block of Winters Lane. It was a popular neighborhood gathering place, where people would come to talk and watch television even if they weren't getting their hair cut.

The first faithful customers were lined up by 5:45 a.m. Saturday, police said. Mr. Peters sat down in the chair, and four other men were waiting for their turn when the woman walked inside. The gunman followed on her heels, pointed his automatic handgun at the men and ordered them to lie down at the back of the shop.

One of the customers shifted nervously when the man opened PTC fire and was shot in the wrist, ankle and leg, police said.

Kevin Michael Johnson, 26, of the 800 block of Augusta Ave., limped outside when the gunman left and called 911 from a pay phone at an Amoco gas station next door. He was released after treatment at the Maryland Shock Trauma Center.

The killings baffled police and shocked neighbors in the quiet, commercial area off Baltimore National Pike.

Detectives were interviewing Mr. Brodie's customers and residents yesterday, trying to determine the motive and get a better description of the suspect.

"At this point in time, it doesn't appear to be a robbery, but we don't have any other clues," said E. Jay Miller, a police spokesman.

The gunman has been described as a black man in his late 20s, about 5 feet 9 inches tall and wearing dark clothing and a dark hat, he said.

Police had no description of the woman, but said she apparently escaped while the men ducked to the floor.

"She's the key to the investigation," Mr. Miller said. "Whether she ran, or whether she had something to do with it, we don't know."

Catonsville residents were frightened and angered by the slayings, which helped push Baltimore County's homicide rate to an all-time high. Thirty-eight people have been killed this year -- four more than in 1988, the deadliest year in county history, Mr. Miller said.

In another attack over the holiday weekend, two men broke into an apartment in the 6600 block of English Oaks Road in Towson and killed Ralph Joseph Spencer, 34, with a handgun. A woman in the apartment who was also shot shortly before midnight Friday was being questioned yesterday by police, who described the shooting as drug-related. Approximately $9,000 was stolen from the apartment, police said.